The invention relates to an MIS-field effect transistor having a short channel length, in which an insulating layer is provided on the surface of a semiconductor member, and which contains a drain electrode and a source electrode respectively extending to the semiconductor surface, and a gate-electrode layer overlying the insulating layer between the drain and source electrodes. In such a construction, a drain zone and a source zone of a first conductivity type extend into the semiconductor member from the contact surfaces of the electrodes, with the source area, at least in a direction towards the drain zone, being surrounded by an additional area of second conductivity type which extends to the semiconductor surface beneath the gate electrode.
Such a MIS-field effect transistor may be designated a "doubly-diffused MIS-FET" and has a short channel length. Doping material of a specific conductivity type is diffused into the semiconductor member through a mask opening in order to produce the short channel, and the doping material in the semiconductor member thereby also extends laterally beyond the borders of the mask opening by means of under-diffusion. The actual source zone is thereafter produced as a result of doping material, of the other conductivity type, being diffused through the same mask opening in a second doping step. By suitable selection of the diffusion temperature and diffusion time, such second doping results in the lateral diffusion, under the edge of the mask, being less than in the first doping step. The two doped areas abut the substrate surface at spaced points, and the portion of the semiconductor substrate disposed between such points, essentially the width by which the first doping was driven deeper into the semiconductor than that of the source-doping, defines the channel across which the gate electrode is arranged. Channel lengths as low as aproximately 1.5 .mu.m can be obtained with such method.
Shorter channel lengths cannot be produced with sufficient reproducibility by this double diffusion method, as the doping profile increasingly widens or expands when doping material is impregnated by means of diffusion. For this reason, a relatively large minimum limit for the obtainable channel length inherently results. In addition, the diffusion is heavily dependent upon temperature, whereby small temperature differentials have a disadvantageous effect in the reproduction capability of such method.
In addition, the relatively low breakthrough voltage in a MIS-FET is disadvantageous for many utilization purposes. For a standard -p-channel MOS-FET, such breakthrough voltage is in the neighborhood of -30 V and is subject to the "field crowding" effect as the electric field in the drain zone becomes increasingly closer to the gate electrodes than the field in the semiconductor member per se, when the breakthrough voltage is exceeded. (See Tokuyama et al in "Microelectronics", 1976, pages 177 through 181.)